Methods of forming interconnects and semiconductor structures

ABSTRACT

A method of activating a metal structure on an intermediate semiconductor device structure toward metal plating. The method comprises providing an intermediate semiconductor device structure comprising at least one first metal structure and at least one second metal structure on a semiconductor substrate. The at least one first metal structure comprises at least one aluminum structure, at least one copper structure, or at least one structure comprising a mixture of aluminum and copper and the at least one second metal structure comprises at least one tungsten structure. One of the at least one first metal structure and the at least one second metal structure is activated toward metal plating without activating the other of the at least one first metal structure and the at least one second metal structure. An intermediate semiconductor device structure is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/401,566, filed Mar. 10, 2009, pending, which is a continuation ofapplication Ser. No. 11/516,193, filed Sep. 6, 2006, now abandoned,which is a continuation of application Ser. No. 10/934,635, filed Sep.2, 2004, now U.S. Pat. No. 7,279,407, issued Oct. 9, 2007, and is alsorelated to application Ser. No. 11/702,286, filed Feb. 5, 2007, now U.S.Pat. No. 7,855,454, issued Dec. 21, 2010. The disclosure of each of thepreviously referenced U.S. patents and patent applications is herebyincorporated by reference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to semiconductor fabrication. Morespecifically, the present invention relates to a method of selectivelyplating aluminum, copper, or tungsten structures with nickel.

Semiconductor devices that have integrated circuits are produced byfabricating a large plurality of identical circuit patterns on asemiconductor wafer using photolithography in combination with variousother processes. It is a continual goal of semiconductor manufacturersto increase the density of semiconductor devices fabricated on a givensize of semiconductor substrate to achieve increased yield ofsemiconductor devices and enhanced performance thereof In recent years,efforts to increase the density of semiconductor devices in asemiconductor assembly have also intensified. One way to increase thedensity of semiconductor devices in a semiconductor assembly is to stacksemiconductor dies upon one another. The semiconductor dies areinterconnected by forming vias or through holes in the semiconductordies. The vias are filled with an electrically conductive material toelectrically connect the vias to integrated circuitry fabricated on anactive surface of the semiconductor die. Thus, the vias provide aconductive pathway from the active surface of the semiconductor die toits respective back surface, enabling interconnection of the backsurface of the semiconductor die to external electrical contacts ofanother semiconductor die or a carrier substrate. The vias are formed byetching, laser ablation or drilling, or a combination thereof. Etchingthe vias utilizes photolithographic processing of a photoresist followedby wet (chemical) or dry (reactive ion) etching. Laser drilling has beenused to form vias by ablating semiconductor material to form throughholes extending through the entire thickness of a semiconductor die.

The vias electrically interconnect various metal interconnectionstructures on the semiconductor die, such as annular rings, bond pads,component leads, metal wires, or other metal layers, to one another.Bond pads on the semiconductor dies are typically formed from aluminum,copper, or aluminum-copper alloys having less than about 0.5% copper.Aluminum is used in bond pads because of its low resistivity, superioradhesion qualities, high thermal stability, and ease of workability.However, one disadvantage of aluminum is that it readily oxidizes toform aluminum oxides, which decrease quality of the electricalconnection and the efficiency of the bond pads. To protect the bondpads, the aluminum is etched to remove the aluminum oxides and coveredwith a barrier metal, such as a nickel layer. Tungsten is also commonlyused as an interconnection material because it has a thermal expansioncoefficient that is similar to that of silicon and has a good fillingcapability in semiconductor structures with high aspect ratios. Tungstenis typically used to fill or line a surface of an opening producedduring formation of a via. The tungsten lining in the via issubsequently covered with a metal layer, such as a nickel layer. Thebond pads are typically nickel plated after vias have been plated withnickel because etchants used to remove the aluminum oxides also removenickel plating from inside the vias.

BRIEF SUMMARY

The present invention relates to a method of selectively plating nickelon an intermediate semiconductor device structure. The method comprisesproviding an intermediate semiconductor device structure comprising atleast one aluminum or copper structure and at least one tungstenstructure on a semiconductor substrate. One of the at least one aluminumor copper structure and the at least one tungsten structure is nickelplated while the other of the at least one aluminum or copper structureand the at least one tungsten structure remains unplated. The nickel maybe plated electrolessly. The at least one aluminum or copper structuremay be at least one aluminum or copper bond pad and the at least onetungsten structure may be at least one via having a layer of tungstentherewithin. In one embodiment, the at least one aluminum or copper bondpad may be nickel plated while the at least one via having a layer oftungsten therewithin remains unplated. In another embodiment, the atleast one via having a layer of tungsten therewithin may be plated withnickel while the at least one aluminum or copper bond pad remainsunplated.

One of the at least one aluminum or copper structure and the at leastone tungsten structure may be plated while the other remains unplated byselecting a nickel plating chemistry selective for one of aluminum,copper, and tungsten. To nickel plate one of the at least one aluminumor copper structure and the at least one tungsten structure while theother remains unplated, one of the at least one aluminum or copperstructure and the at least one tungsten structure may be activatedtoward nickel plating. The at least one aluminum or copper structure maybe activated by exposing the intermediate semiconductor device structureto a zincate solution. The zincate solution may be an aqueous solutioncomprising zinc oxide and sodium hydroxide. The at least one tungstenstructure may be activated toward nickel plating by exposing theintermediate semiconductor device structure to a palladium solution. Thepalladium solution may be an aqueous solution comprising palladium (II)ions.

The activated one of the at least one aluminum or copper structure andthe at least one tungsten structure may be nickel plated by immersingthe intermediate semiconductor device structure in an electroless nickelplating solution that comprises a nickel salt selected from the groupconsisting of nickel sulfate, nickel chloride, nickel sulfate, nickelbromide, nickel fluoroborate, nickel sulfonate, nickel sulfamate, andnickel alkyl sulfonate and a reducing agent selected from the groupconsisting of sodium hypophosphite, dimethylamine borane, sodiumborohydride, and dimethylaminobenz-aldehyde (“DMAB”). The unplated oneof the at least one aluminum or copper structure and the at least onetungsten structure may subsequently be nickel plated by activating theunplated structure and then nickel plating the activated structure.

The present invention also relates to an intermediate semiconductordevice structure that comprises a semiconductor substrate comprising atleast one aluminum or copper structure and at least one tungstenstructure. One of the at least one aluminum or copper structure and theat least one tungsten structure is plated with nickel while the other ofthe at least one aluminum or copper structure and the at least onetungsten structure remains unplated. The at least one aluminum or copperstructure may be at least one aluminum or copper bond pad and the atleast one tungsten structure may be at least one via having a layer oftungsten therewithin. The at least one via having a layer of tungstentherewithin may be a through-wafer-interconnect or ablind-wafer-interconnect.

The present invention also relates to an intermediate semiconductordevice structure that comprises a semiconductor substrate comprising atleast one aluminum or copper structure having a first nickel layerplated thereon and at least one tungsten structure having a secondnickel layer plated thereon. At least one of the first nickel layer andthe second nickel layer is formed by formulating a nickel platingchemistry selective for one of the at least one aluminum or copperstructure and the at least one tungsten structure. The at least onealuminum or copper structure may be at least one aluminum or copper bondpad and the at least one tungsten structure may be at least one viahaving a layer of tungsten therewithin. The at least one via having alayer of tungsten therewithin may be a through-wafer-interconnect or ablind-wafer-interconnect.

The nickel plating chemistry selective for the at least one aluminum orcopper structure may include an aluminum or copper activator and anelectroless nickel plating solution. The aluminum or copper activatormay be a zincate solution, as previously described, and the electrolessnickel plating solution may be as previously described. The nickelplating chemistry selective for the at least one tungsten structure mayinclude a tungsten activator and an electroless nickel plating solution.The tungsten activator may be a palladium solution, as previouslydescribed, and the electroless nickel plating solution may be aspreviously described.

The present invention also relates to a method of plating nickel on anintermediate semiconductor device structure. The method comprisesproviding an intermediate semiconductor device structure comprising atleast one aluminum or copper structure and at least one tungstenstructure on a semiconductor substrate. The at least one aluminum orcopper structure and the at least one tungsten structure aresimultaneously plated with nickel. The at least one aluminum or copperstructure and the at least one tungsten structure may be nickel platedby activating a surface of the at least one aluminum or copper structureand the at least one tungsten structure. To activate the surface of theat least one aluminum or copper structure, the intermediatesemiconductor device structure may be exposed to a zincate solution, aspreviously described. To activate the surface of the at least onetungsten structure, the intermediate semiconductor device structure maybe exposed to a palladium solution, as previously described. Theactivated, at least one aluminum or copper structure and the activated,at least one tungsten structure are simultaneously plated with nickel byimmersing the intermediate semiconductor device structure in anelectroless nickel plating solution, as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention may be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIGS. 1, 3-8, 10, 12, 14, and 16 schematically illustrate a crosssectional view of one embodiment of an integrated circuit in which athrough-wafer-interconnect is formed;

FIGS. 17-20 schematically illustrate a cross sectional view of anotherembodiment of an integrated circuit in which athrough-wafer-interconnect is formed; and

FIGS. 2, 9, 11, 13, and 15 schematically illustrate a cross sectionalview of an embodiment of an integrated circuit in which ablind-wafer-interconnect is formed.

DETAILED DESCRIPTION

A method of selectively plating nickel on either an aluminum structureor a tungsten structure present on a semiconductor substrate isdisclosed. The semiconductor substrate includes both the aluminumstructure and the tungsten structure. In one embodiment, the aluminumstructure is plated with nickel without depositing nickel on thetungsten structure. The aluminum structure is nickel plated with anickel plating chemistry that is selective for aluminum. As used herein,the term “nickel plating chemistry” includes chemistries that are usedto clean the structures, activate the structures, or plate thestructures with nickel. In another embodiment, the tungsten structuremay be plated with nickel without nickel plating the aluminum structureutilizing a nickel plating chemistry that is selective for tungsten. Inanother embodiment, the tungsten structure and the aluminum structuremay be substantially simultaneously plated with nickel.

The nickel may be deposited on either the aluminum structure or thetungsten structure by electroless plating. To deposit the nickel, eitherthe aluminum structure or the tungsten structure may be activated towardnickel plating by exposing the structures to an activator that isselective for either aluminum or tungsten. For instance, if the aluminumstructure is to be nickel plated, the activator may be selective foraluminum. Conversely, if the tungsten structure is to be nickel plated,the activator may be selective for tungsten. A surface of the activatedstructure may then be plated with nickel while a surface of theunactivated structure remains unplated. The unplated surface maysubsequently be plated with nickel by exposing the structures to adifferent nickel plating chemistry, such as a different activator, thatis selective for the unplated surface. Once activated, the unplatedsurface may be nickel plated.

By exposing the structures to the activator selective for aluminum ortungsten, the aluminum structure or the tungsten structure may beactivated and plated with nickel while the unactivated structure remainsunplated. For instance, if the structures are exposed to an activatorthat is selective for aluminum, nickel may be electrolessly plated onthe aluminum structure without nickel plating the tungsten structure.After nickel plating the aluminum structure, nickel may be plated on thetungsten structure using a different nickel plating chemistry.Similarly, if the structures are exposed to an activator that isselective for tungsten, nickel may be electrolessly plated on thetungsten structure without plating the aluminum structure. Nickel maysubsequently be plated on the aluminum structure using a differentnickel plating chemistry.

While the embodiments disclosed herein describe that the aluminumstructure is an aluminum bond pad and the tungsten structure is atungsten-lined via, the present invention may also be used toselectively plate nickel on additional aluminum or tungsten structures.

The nickel may be selectively plated on an intermediate semiconductordevice structure 2 that has at least one aluminum structure and at leastone tungsten structure. The tungsten structure may be a via 4 lined withtungsten and the aluminum structure may be a bond pad 6, as shown inFIGS. 1 and 2. As used herein, the term “via” refers to an opening in asemiconductor substrate 8 that is subsequently filled or lined with aconductive material to provide a conductive pathway through thesemiconductor substrate 8. For the sake of clarity, one via 4 and twobond pads 6 are shown in FIGS. 1 and 2. However, the intermediatesemiconductor device structure 2 may include a plurality of vias 4 and aplurality of bond pads 6. The via 4 and the bond pads 6 may both bepresent on an exterior or exposed surface of the intermediatesemiconductor device structure 2 and, as such, may both be exposed. Thebond pad 6 may be formed on the semiconductor substrate 8 from aconductive metal, such as aluminum, by conventional techniques. The bondpad 6 may have a thickness ranging from approximately 1.0 μm toapproximately 1.5 μm. The via 4 may be filled or lined with theconductive material to provide the conductive pathway. The via 4 mayextend through an entire thickness of the semiconductor substrate 8, asshown in FIG. 1, or may form a blind hole in the semiconductor substrate8, as shown in FIG. 2. If the via 4 extends through the thickness of thesemiconductor substrate 8, the via 4 may be referred to as athrough-wafer-interconnect (“TWI”). The TWI may electrically connectintegrated circuits on one side of the semiconductor substrate toanother component or apparatus on the opposing side. If the via 4 formsa blind hole in the semiconductor substrate, the via 4 may be referredto as a blind-wafer-interconnect (“BWI”).

The intermediate semiconductor device structure 2 may also include asemiconductor substrate 8, a first oxide layer 10 covering a surface ofthe semiconductor substrate 8, and a passivation layer 12 coveringportions of the first oxide layer 10, as shown in FIG. 3. Thesemiconductor substrate 8 may be a semiconductor wafer or other bulksubstrate that includes a layer of semiconductive material. The term“bulk substrate” as used herein includes not only silicon wafers (e.g.monocrystalline silicon or polycrystalline silicon), but silicon oninsulator (“SOI”) substrates, silicon on sapphire (“SOS”) substrates,silicon on glass (“SOG”) substrates, epitaxial layers of silicon on abase semiconductor foundation, and other semiconductor materials, suchas silicon-germanium, germanium, ruby, quartz, sapphire, galliumarsenide, diamond, silicon carbide, or indium phosphide. The first oxidelayer 10 may be a silicon oxide layer, such as a layer of phosphorussilicate glass (“PSG”), borosilicate glass (“BSG”), borophosphosilicateglass (“BPSG”), or spin-on dielectric (“SOD”). In one embodiment, thefirst oxide layer 10 is a BPSG layer. The passivation layer 12 may beformed from silicon dioxide (“SiO₂”), silicon nitride (“SiN”), siliconoxynitride, BPSG, PSG, BSG, a polyimide, benzocyclobutene, mixturesthereof, or another nonconductive material as known in the art. In oneembodiment, the passivation layer 12 is a sandwich structure of SiO₂ andSiN, as known in the art. The passivation layer 12 may have a thicknessranging from approximately 0.5 μm to 10 μm. The first oxide layer 10 andthe passivation layer 12 may have been previously formed on thesemiconductor substrate 8 by conventional techniques.

If the via 4 is to be a TWI, the via 4 may be formed in the intermediatesemiconductor device structure 2 by forming at least one opening 14 thatextends through a thickness of the semiconductor substrate 8, asillustrated in FIGS. 3-7. The opening 14 may be formed by laser drillingor ablation, dry etching, such as a reactive ion etch, photochemicaletching, masking and anisotropic etching, mechanical drilling, or anyother known process of forming openings in semiconductor substrates 8.For the sake of example only, the opening 14 may be formed by depositinga photoresist layer 16 over the bond pads 6 and the passivation layer12. The photoresist layer 16 may be etched to expose at least a portionof the bond pad 6, as shown in FIG. 4. The photoresist layer 16 may be aconventional photoresist and is deposited by conventional techniques.The exposed portion of the bond pad 6 may be removed to expose at leasta portion of the first oxide layer 10. The exposed portion of the firstoxide layer 10 may be removed as shown in FIG. 5 to expose a portion ofthe semiconductor substrate 8, which is subsequently removed to form theopening 14, as shown in FIG. 6. Remaining portions of the photoresistlayer 16 may then be removed as shown in FIG. 7. Alternatively, theexposed portion of the first oxide layer 10 and an underlying portion ofthe semiconductor substrate 8 may be etched substantially simultaneouslyto form the opening 14. The resulting opening 14 may have a high aspectratio ranging from approximately 4:1 (substrate thickness:via diameter)to approximately 30:1.

Alternatively, the opening 14 may be formed by etching a hole throughthe bond pad 6 using a wet etch chemistry, as known in the art. The holemay be extended using a dry oxide etch, such as by reactive ion etching(“RIE”), to etch the first oxide layer 10 and expose the semiconductorsubstrate 8. A dimple may be fowled in the semiconductor substrate 8with a wet etch chemistry that includes a solution oftetramethylammonium hydroxide (“TMAH”) and an organic solvent, such aspropylene glycol. The dimple may range in size from approximately 10 μmto approximately 15 μm. The etch solution may include from approximately1% by weight to approximately 10% by weight of TMAH and fromapproximately 90% by weight to approximately 99% by weight of theorganic solvent. In one embodiment, the etch solution includesapproximately 6% TMAH and approximately 94% propylene glycol.

The hole may be extended through the semiconductor substrate 8 by laserablating a portion of the semiconductor substrate 8. The semiconductorsubstrate 8 may be laser ablated by directing a laser beam toward thedimple from a back surface of the semiconductor substrate 8. The dimplemay keep energy produced by the laser beam from an active surface of theintegrated circuit. The energy from the laser beam may ablate theportion of the semiconductor substrate 8, extending the hole and formingthe opening 14. However, the energy from the laser beam may unduly heatthe semiconductor substrate 8 surrounding the opening 14 and produce aheat affected zone (“HAZ”), which is an area of damaged siliconsurrounding the opening 14. The material of the HAZ is commonly referredto as a “slag” and may include silicon and oxygen. The dimple formed inthe semiconductor substrate 8 may also prevent slag from being depositedon the active surface of the integrated circuit. The HAZ may be removedso that the opening 14 has a sufficient width or diameter to form thenecessary conductive path. The HAZ may be removed using the TMAH andpropylene glycol etch solution previously described. This etch solutionmay selectively remove the HAZ without damaging other portions of theintegrated circuit, such as the bond pad 6 or the first oxide layer 10.

The photoresist layer 16, the exposed portions of the bond pads 6, theexposed portions of the first oxide layer 10, and the exposed portionsof the semiconductor substrate 8 may be removed from the intermediatesemiconductor device structure 2 by using conventional dry etchchemistries, conventional wet etch chemistries, or a laser etch. Theetching techniques and conditions may be selected by one of ordinaryskill in the art based on the materials used in each of these layers.Therefore, the etching techniques and conditions are not discussed indetail herein. For sake of example only, the first oxide layer 10 may beetched using a plasma etch with a tetrafluoromethane (“CF₄”) chemistryor a trifluoromethane (“CHF₃”) and oxygen (“O₂”) chemistry.Alternatively, the first oxide layer 10 may be etched with an aqueoussolution of dilute hydrogen fluoride (“HF”). The semiconductor substrate8 may be etched using a plasma etch with a NF₃, HBr/Cl, C₂F₄, or SF₆chemistry.

The opening 14 may be lined with a second oxide layer 18 to sealportions of the semiconductor substrate 8 that are exposed when theopening 14 is formed. The second oxide layer 18 may be formed from a lowstress or low Si oxide (“LSO”), which is deposited on the semiconductorsubstrate 8 by conventional techniques. The second oxide layer 18 may bedeposited at a thickness ranging from 0.1 μm to approximately 5 μm, suchas from approximately 1 μm to approximately 2 μm. A tungsten layer 20may be formed over the second oxide layer 18 to provide a seed layerupon which the nickel is subsequently deposited. The tungsten layer 20may have a thickness ranging from approximately 0.02 μm to approximately1 μm. The tungsten layer 20 may be formed by atomic layer deposition(“ALD”), electroless deposition, electroplating, chemical vapordeposition (“CVD”), plasma-enhanced CVD (“PECVD”), or physical vapordeposition (“PVD”), as known in the art. An adhesion layer mayoptionally be present between the tungsten layer 20 and the second oxidelayer 18 to more firmly adhere the tungsten layer 20 to the second oxidelayer 18. The adhesion layer may be formed by ALD, CVD, PECVD, PVD,vacuum evaporation, or sputtering. In one embodiment, the adhesion layeris formed from titanium nitride (“TiN”). The adhesion layer may have athickness ranging from approximately 50 Å to approximately 200 Å. Theadhesion layer may be used in the opening 14 depending on a thickness ofthe tungsten layer 20. If the tungsten layer 20 is less thanapproximately 500 Å thick, the adhesion layer may not be needed toadhere the tungsten layer 20 to the second oxide layer 18. However, ifthe tungsten layer 20 is greater than approximately 500 Å thick, theadhesion layer may be used to adequately adhere the tungsten layer 20 tothe second oxide layer 18.

If the via 4 is to be a BWI, the via 4 may be formed in the intermediatesemiconductor device structure 2 by forming at least one opening 14 thatextends a selected depth into the semiconductor substrate 8, as shown inFIG. 2. In this situation, the opening 14 may be formed as describedabove, except that the opening 14 does not extend through the entirethickness of the semiconductor substrate 8. The opening 14 may be linedwith the second oxide layer 18 and the tungsten layer 20, as describedabove.

As shown in FIGS. 8 and 9, the second oxide layer 18, the tungsten layer20, and the adhesion layer (if present) of the intermediatesemiconductor device structure 2 may be etched to remove portions ofthese layers overlying the bond pads 6 and the passivation layer 12.Portions of the second oxide layer 18 and the tungsten layer 20 mayremain in the via 4. This etch step is referred to herein as a “spaceretch.” The etching techniques and conditions used to remove the secondoxide layer 18, the tungsten layer 20, and the adhesion layer (ifpresent) may be selected by one of ordinary skill in the art based onthe materials in these layers and, therefore, are not discussed indetail herein. For sake of example only, the tungsten layer 20 and theadhesion layer (if present) may be removed with a conventional dry etch.The second oxide layer 18 may be removed with a conventional wet etch.

A first nickel layer 22 may then be plated on the exposed bond pads 6without plating nickel on the tungsten layer 20, as shown in FIGS. 10and 11. To form the first nickel layer 22, the surface of the bond pads6 may be cleaned to remove aluminum oxides. By way of example, acleaning solution used to remove the aluminum oxides may be an aqueoussolution of sodium hydroxide (“NaOH”) and nitric acid (“HNO₃”) orphosphoric acid. The NaOH may dissolve the aluminum oxides on thesurface of the bond pads 6 while the HNO₃ or phosphoric acid may etchthe surface of the bond pads 6 to provide a clean aluminum surface uponwhich the first nickel layer 22 is ultimately plated. The cleaningsolution may include from approximately 1% to approximately 5% NaOH andapproximately 50% HNO₃, with the remainder being water. The bond pads 6may be cleaned by immersing the intermediate semiconductor devicestructure 2 in the cleaning solution or by spraying the intermediatesemiconductor device structure 2 with the cleaning solution. The bondpads 6 may then be rinsed with deionized water to remove the NaOH andHNO₃ or phosphoric acid. Other wet etches known in the art to remove thealuminum oxide formed on the bond pads 6 may also be employed.

After removing the aluminum oxides, the surface of the bond pads 6 maybe activated toward nickel plating using an activator that is selectivefor aluminum. Since the aluminum activator is selective for aluminum,the surface of the tungsten layer 20 may not be activated toward nickelplating. The aluminum activator may be an aqueous zincate solution thatincludes a zinc source material, such as zinc oxide (“ZnO”), and acaustic base, such as NaOH or another alkali metal hydroxide. Atalkaline pH, the zinc source material may be present in the zincatesolution as Zn(OH)₄. The intermediate semiconductor device structure 2may be exposed to the zincate solution for an amount of time sufficientto deposit a zinc-containing layer on the surface of the bond pads 6.The zinc-containing layer may include from approximately one monolayerto approximately two monolayers of a layer rich in zinc. Thezinc-containing layer may function as a seed layer to the first nickellayer 22. The intermediate semiconductor device structure 2 may beexposed to the zincate solution for from approximately 10 seconds toapproximately 1 minute. Zincate solutions are commercially availablefrom various manufacturers, such as from LeaRonal Inc. (Buffalo, N.Y.)or PacTech GmbH (Berlin, Germany). The bond pads 6 of the intermediatesemiconductor device structure 2 may be activated by immersing theintermediate semiconductor device structure 2 in the aluminum activatoror spraying the intermediate semiconductor device structure 2 with thealuminum activator. The aluminum activator may be maintained at atemperature ranging from approximately 20° C. to approximately 40° C.

Once the bond pads 6 are activated toward nickel plating, theintermediate semiconductor device structure 2 may be rinsed withdeionized water and immersed in a bath containing the electroless nickelplating solution to form the first nickel layer 22. The first nickellayer 22 may act as a wetting layer that enables molten solder to moreeffectively fill the via 4. The first nickel layer 22 may also act as abarrier layer. Electroless nickel plating solutions are known in theart, such as electroless nickel-phosphorus plating solutions orelectroless nickel-boron plating solutions. Such electroless nickelplating solutions are commercially available, such as NicPac 2.1, NicPac2.2, and NicPac 2.3, which are available from PacTech GmbH (Berlin,Germany) and RONAMAX® SMT, DURAPOSIT®, NIPOSIT®, NIPLATE™, which areavailable from Rohm and Haas Electronic Materials (Philadelphia, Pa.).These electroless nickel plating solutions include nickel salts, such asnickel sulfate, nickel chloride, nickel sulfate, nickel bromide, nickelfluoroborate, nickel sulfonate, nickel sulfamate, and nickel alkylsulfonates, as a source of the nickel ion. The electroless nickelplating solution may also include a reducing agent, such as a phosphoruscompound or a boron compound. Examples of reducing agents include sodiumhypophosphite, dimethylamine borane, sodium borohydride, and DMAB. Theelectroless nickel plating solution may also include NaOH to maintainthe pH of the solution and complexing agents, such as citric acid,lactic acid, or malic acid. The pH of the electroless nickel platingsolution may be maintained from approximately 4 to approximately 6.During the electroless plating, nickel ions are reduced to nickel byoxidation of the reducing agent. In one embodiment, the electrolessnickel plating solution includes nickel chloride, sodium hydroxyacetate,and sodium hypophosphite. In another embodiment, the electroless nickelplating solution includes nickel sulfate and sodium hypophosphite. Theelectroless nickel plating solution in the bath may be maintained at atemperature ranging from approximately 60° C. to approximately 100° C.,such as from approximately 80° C. to approximately 90° C.

A thickness of the first nickel layer 22 on the bond pads 6 may dependon the concentration of nickel in the electroless nickel platingsolution and an amount of time the intermediate semiconductor devicestructure 2 is immersed in the electroless nickel plating solution. Thefirst nickel layer 22 may have a thickness ranging from approximately500 Å to approximately 10 μm. In one embodiment, the first nickel layer22 has a thickness of approximately 1 μm. The intermediate semiconductordevice structure 2 may be immersed in the electroless nickel platingsolution for an amount of time sufficient to deposit the desiredthickness of the first nickel layer 22 on the bond pad 6, such as fromapproximately 1 minute to approximately 5 minutes. During the nickelplating, the zinc-containing layer on the bond pad 6 may be replacedwith the first nickel layer 22. Since the nickel plating chemistry isselective for aluminum, the bond pad 6 may be substantially plated withnickel, while substantially no nickel is plated on the tungsten layer 20in the via 4.

Since the nickel plating chemistry may be used to plate directly oncopper, bond pads 6 formed from copper may be selectively plated withnickel without nickel plating the tungsten layer 20. Activation of thebond pads 6 formed from copper may occur substantially as describedabove in regard to the aluminum bond pad 6. Alternatively, the copperbond pad 6 may be activated with a palladium solution before nickelplating, rather than with the zincate solution.

After the first nickel layer 22 has been formed over the bond pads 6,the second nickel layer 24 may be deposited in the opening 14 to linethe via 4, as shown in FIGS. 12 and 13. The second nickel layer 24 mayact as a wetting layer to enable the molten solder to more effectivelyfill the via 4. The second nickel layer 24 may be deposited over thetungsten layer 20 after first removing oxides from the tungsten layer20. The tungsten layer 20 may be cleaned chemically, such as by using anaqueous potassium hydroxide (“KOH”) solution.

The tungsten layer 20 may then be activated toward nickel plating withan activator that is selective for tungsten. Since the tungstenactivator is selective for tungsten, the bond pads 6 may not beactivated toward nickel plating. The tungsten activator may be anaqueous palladium solution that includes palladium (II) ions. Theintermediate semiconductor device structure 2 may be exposed to thetungsten activator for a sufficient amount of time to deposit a thinlayer of palladium on the surface of the tungsten layer 20. Forinstance, the intermediate semiconductor device structure may be exposedto the tungsten activator for from approximately 10 seconds toapproximately 1 minute. The tungsten layer 20 of the intermediatesemiconductor device structure 2 may be activated by immersing theintermediate semiconductor device structure 2 in the tungsten activatoror spraying the intermediate semiconductor device structure 2 with thetungsten activator.

After the tungsten layer 20 is activated toward nickel plating, theintermediate semiconductor device structure 2 may be immersed in a bathcontaining the electroless nickel plating solution to form the secondnickel layer 24 on the tungsten layer 20. The electroless nickel platingsolution may be a conventional nickel plating solution. The electrolessnickel plating solution may be the same electroless nickel platingsolution as used to plate the first nickel layer 22 or may be adifferent electroless nickel plating solution. The electroless nickelplating solutions are as previously described. The second nickel layer24 may have a thickness ranging from approximately 500 Å toapproximately 10 μm. In one embodiment, the second nickel layer 24 has athickness ranging from approximately 3 μm to approximately 5 μm. Theintermediate semiconductor device structure 2 may be immersed in theelectroless nickel plating solution for an amount of time sufficient todeposit the desired thickness of the second nickel layer 24 on the bondpad 6, such as from approximately 1 minute to approximately 5 minutes.During the nickel plating, the layer of palladium on the tungsten layer20 may be replaced with the second nickel layer 24. Since theelectroless nickel plating solution is selective for tungsten, thetungsten layer 20 may be substantially plated with nickel whilesubstantially no nickel is plated on the bond pads 6.

The via 4 may then be filled with solder 26 to provide the conductivepathway, as shown in FIGS. 14 and 15. The solder may be a conventionalsolder formulation that includes tin, lead, indium, antimony, silver,copper, and mixtures thereof. The solder may be capable of wetting orfilling the via 4. Suitable solder formulations may include, but are notlimited to 95% lead/5% tin, 60% lead/40% tin, 63% indium/37% tin, 100%tin, and 62% lead/36% tin/2% silver. To fill the via 4 with the solder26, the solder 26 may be heated to a temperature sufficient to melt thesolder 26, such as from 180° C. to approximately 300° C. The moltensolder may then be deposited in the via 4 or near the bond pads 6. Ifthe molten solder is deposited near the bond pads 6, it may be reflowedinto the via 4 to provide the conductive path. The solder 26 may also bedeposited using a wave solder process in which the molten solder isapplied to a back surface of the intermediate semiconductor devicestructure 2, if the via 4 is a TWI. The molten solder may then be drawninto the via 4 by capillary action and wetting forces.

If the via 4 is a BWI, a mass of solder, such as a solder ball, may beplaced at the mouth of the via 4, melted, and drawn into the via 4 bycapillary action. A back surface of the semiconductor substrate 8 may beremoved, as shown in FIG. 16, to expose the via 4. The back surface ofthe semiconductor substrate 8 may be removed by backgrinding, as knownin the art. Backgrinding of the semiconductor substrate 8 may beachieved by chemical mechanical polishing (“CMP”) or by abrasive means.After removing the back surface, the via 4 may extend through thethickness of the semiconductor substrate 8, forming a TWI. As such, theTWI may be formed directly or may be formed after first forming the BWI.

Alternatively, the first nickel layer 22 may be formed over the bondpads 6, as shown in FIG. 17. The first nickel layer 22 may be formed aspreviously described. Then, the opening 14 may be formed in thesemiconductor substrate 8, as shown in FIG. 18. The opening 14 may beformed as previously described. The second oxide layer 18, the tungstenlayer 20, and, optionally, the adhesion layer, may then be deposited inthe opening 14 to form the via 4. As shown in FIG. 19, the second oxidelayer 18, the tungsten layer 20, and the adhesion layer (if present) maybe removed from the surface of the intermediate semiconductor devicestructure 2 using the spacer etch. The second nickel layer 24 may thenbe plated over the tungsten layer 20, as shown in FIG. 20. The secondnickel layer 24 may be plated as previously described. The via 4 maythen be filled with solder 26, as previously described in regard to FIG.14. By depositing the first nickel layer 22 over the bond pads 6 beforethe via 4 is formed, nickel may not be deposited on portions of thesemiconductor substrate 8 that are exposed after the opening 14 isformed.

By depositing the first nickel layer 22 on the aluminum structure beforedepositing the second nickel layer 24 on the tungsten structure, thealuminum structure may be protected during subsequent processing steps.For instance, the first nickel layer 22 may act as a nickel mask toprotect the aluminum structure from exposure to the tungsten activator.The tungsten structure may then be nickel plated without furtherprotecting the aluminum structure. In addition, since the tungstenstructure is nickel plated after nickel plating the aluminum structure,nickel is not removed from the tungsten structure by the cleaning,activating, and plating chemistries used to plate the aluminumstructure. In other words, the etching chemistry used to remove thealuminum oxides may not remove portions of the second nickel layer 24from inside the via 4.

As previously mentioned, in another embodiment, the tungsten structureis plated with nickel before nickel plating the aluminum structure. Thetungsten structure may be selectively plated with nickel by activatingthe tungsten structure toward nickel plating and subsequently depositingthe nickel, as previously described. The aluminum structure may then benickel plated by activating the aluminum structure toward nickel platingand subsequently depositing the nickel, as previously described.

In another embodiment, the tungsten structure and the aluminum structureare plated with nickel substantially simultaneously by activating thesurfaces of both the tungsten structure and the aluminum structurebefore nickel plating. The aluminum structure may be activated byexposing the intermediate semiconductor device structure 2 to thezincate solution, as previously described. The intermediatesemiconductor device structure 2 may then be exposed to the tungstenactivator to activate the tungsten structure. The activated tungstenstructure and the aluminum structure may then be nickel plated, aspreviously described.

In addition to selectively plating one of the aluminum structure and thetungsten structure with nickel, the method of the present invention mayalso be used to selectively plate one of a copper structure and thetungsten structure with nickel. As such, the bond pad 6 may be formedfrom copper or mixtures of aluminum and copper. Since conventionalnickel plating chemistries may be plated directly onto copper, the bondpad 6 formed from copper may be selectively plated with nickel.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

What is claimed is:
 1. A method of forming a semiconductor structure,comprising: selectively forming nickel over a tungsten material on asubstrate without forming the nickel over one or more of an aluminummaterial and a copper material on the substrate; activating the aluminummaterial or the copper material to nickel plating; and forming nickelover an exposed surface of the aluminum material or the copper material.2. The method of claim 1, wherein selectively forming nickel over atungsten material on a substrate without forming the nickel over one ormore of an aluminum material and a copper material comprises: exposingthe substrate to a palladium(II) solution to activate the tungstenmaterial without activating the aluminum material or the coppermaterial; and exposing the substrate to a nickel plating solution. 3.The method of claim 1, wherein forming nickel over an exposed surface ofthe aluminum material or copper material comprises: exposing thesubstrate to a zincate solution to activate the aluminum material or thecopper material; and exposing the substrate to a nickel platingsolution.
 4. The method of claim 1, wherein selectively forming nickelover a tungsten material on a substrate without forming the nickel overone or more of an aluminum material and a copper material on thesubstrate comprises forming the nickel over an exposed tungsten liningwithout forming the nickel over an exposed aluminum bond pad or anexposed copper bond pad.
 5. A method of forming an interconnect in asemiconductor structure, comprising: removing a portion of asemiconductor substrate to form a via at least partially extendingtherethrough, the semiconductor substrate having at least one metalstructure comprising at least one of aluminum and copper disposedthereon; forming tungsten over surfaces exposed within the via;selectively forming nickel over the tungsten within the via withoutforming nickel over the at least one of aluminum and copper of the atleast one metal structure; activating the at least one of aluminum andcopper of the at least one metal structure to nickel plating; andforming nickel over an exposed surface of the at least one of aluminumand copper of the at least one metal structure.
 6. The method of claim5, further comprising filling the remaining portions of the via withsolder.
 7. The method of claim 5, further comprising forming at leastone of an oxide material and an adhesion material over surfaces exposedwithin the via before forming the tungsten.
 8. The method of claim 5,wherein forming tungsten over surfaces exposed within the via compriseslining the surfaces exposed within the via with the tungsten.
 9. Themethod of claim 5, wherein forming tungsten over surfaces exposed withinthe via comprises forming tungsten over surfaces of at least one of abond pad, an oxide material, and the semiconductor substrate exposedwithin the via.
 10. The method of claim 5, wherein selectively formingnickel over the tungsten within the via comprises: activating thetungsten toward nickel plating without activating the at least one ofaluminum and copper; and exposing the tungsten to a nickel platingsolution.
 11. The method of claim 10, wherein activating the tungstentoward nickel plating without activating the at least one of aluminumand copper comprises activating the tungsten by exposing thesemiconductor structure to an aqueous solution comprising palladium(II)ions.
 12. The method of claim 11, further comprising exposing thetungsten to an aqueous potassium hydroxide solution before activatingthe tungsten toward the nickel plating.
 13. The method of claim 5,wherein selectively forming nickel over the tungsten comprises exposingthe tungsten over the surfaces exposed within the via to a nickelplating solution.
 14. The method of claim 4, further comprising exposingthe at least one metal structure to an aqueous solution comprisingsodium hydroxide and at least one of nitric acid and phosphoric acid.15. A method of forming an interconnect, comprising: forming tungstenover an oxide material lining surfaces within a via extending at leastpartially through a semiconductor substrate; forming nickel on thetungsten within the via without forming nickel on at least one exposedbond pad comprising at least one of aluminum and copper; activating theat least one exposed bond pad toward nickel plating; forming nickel onthe at least one exposed bond pad; and filling the via with at least oneconductive material.
 16. The method of claim 15, wherein formingtungsten over an oxide material lining surfaces within a via extendingat least partially through a semiconductor substrate comprises formingthe tungsten on a titanium nitride material overlying the oxidematerial.
 17. The method of claim 15, wherein forming nickel on thetungsten within the via without forming nickel on at least one exposedbond pad comprises: exposing the semiconductor structure to apalladium(II) solution to activate the tungsten without activating theat least one exposed bond pad; and exposing the semiconductor structureto a nickel plating solution.
 18. The method of claim 17, wherein the atleast one exposed bond pad comprises aluminum, and wherein exposing thesemiconductor structure to a palladium(II) solution to activate thetungsten without activating the at least one exposed bond pad comprisesactivating the tungsten without activating the aluminum.
 19. The methodof claim 15, wherein forming nickel on the at least one exposed bond padcomprises: exposing the semiconductor structure to a zincate solution toactivate the at least one exposed bond pad; and exposing thesemiconductor structure to a nickel plating solution.
 20. The method ofclaim 15, further comprising removing a portion of the semiconductorsubstrate from a backside of the semiconductor structure to expose thevia filled with the at least one conductive material.
 21. A method offorming an interconnect in a semiconductor structure, comprising:removing portions of each of a bond pad comprising at least one ofaluminum and copper and a semiconductor substrate to form a viaextending through the bond pad and at least partially into thesemiconductor substrate; forming an oxide material over surfaces exposedwithin the via; forming tungsten over the oxide material; contacting thetungsten with a nickel plating solution to form nickel over the tungstenwithout forming nickel over the bond pad; activating the bond pad towardnickel plating; contacting the activated bond pad with a nickel platingsolution to form nickel over the activated bond pad; and filling the viawith a conductive material.
 22. The method of claim 21, whereincontacting the activated bond pad with a nickel plating solution to formnickel over the activated bond pad comprises nickel plating portions ofthe bond pad exposed through a passivation material.